Dielectric ceramic and manufacturing method therefor and laminated ceramic capacitor

ABSTRACT

A laminated ceramic capacitor is provided which is excellent in reliability even when its dielectric ceramic layers thinned. For a dielectric ceramic in a laminated ceramic capacitor, a ceramic is used which includes a main component containing a barium titanate based composite oxide represented by the general formula: (Ba 1-h-m-x Ca h Sr m Re x ) k (Ti 1-n-y Zr n M y )O 3 , where Re is La or the like, M is Mg or the like, and the respective relationships of 0.05≦x≦0.50, 0.02≦y≦0.3, 0.85≦k≦1.05, 0≦h≦0.25, 0≦m≦0.50, and 0≦n≦0.40 are satisfied; and an accessory component as a sintering aid, wherein the average grain diameter of crystal grains in a sintered body is 0.6 μm or less.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a dielectric ceramic, a method formanufacturing the dielectric ceramic, and a laminated ceramic capacitorcomposed with use of the dielectric ceramic, and in particular, relatesto an improvement for enhancing the reliability of the laminated ceramiccapacitor.

2. Description of the Related Art

While a variety of rated voltages are used for laminated ceramiccapacitors, high insulation properties (insulation resistance) andreliability (lifetime characteristics in a high temperature load test)are required for the ceramic material constituting dielectric ceramiclayers of, in particular, laminated ceramic capacitors to which middleto high voltages (several tens V to several hundreds V) are applied.

In addition, in the past several years, the need for reduction in sizeof laminated ceramic capacitors has increased. Thus, in order to ensureat least a predetermined capacitance in the case of small sizes, thinnerdielectric ceramic layers have been demanded. However, the thinner thedielectric ceramic layers are, the higher is the intensity of anelectric field applied to each of the dielectric ceramic layers. Thehigher intensity effects achieving the reliability, in particular,higher lifetime characteristic in a load test, which has been requiredfor the dielectric ceramic.

Dielectric ceramics which can satisfy such demands are disclosed, forexample, in International Publication No. WO2004/067473.

International Publication No. WO2004/067473 discloses a dielectricceramic containing: a main component composed of barium titanate basedcomposite oxide with some Ba substituted with Gd and some Ti substitutedwith Mg, which is represented by the general formula:(Ba_(1-h-i-m)Ca_(h)Sr_(i)Gd_(m))_(k) (Ti_(1-y-j-n)Zr_(y)Hf_(j)Mg_(n)) O₃and satisfies respective relationships of 0.995≦k≦1.015, 0≦h≦0.03,0≦i≦0.03, 0.015≦m≦0.035, 0≦y<0.05, 0≦j<0.05, 0≦y+j)<0.05, and0.015≦n≦0.035; and addition components of Ma (Ma is at least one of Ba,Sr, and Ca) at less than 1.5 moles, however, excluding 0 moles, withrespect to 100 moles of the main component, Mb (Mb is at least one of Mnand Ni) at less than 1.0 mole, however, excluding 0 moles, with respectto 100 moles of the main component, and Mc (Mc is Si, or both Si and Ti)at 0.5 moles or more and 2.0 moles or less with respect to 100 moles ofthe main component.

The main component of the dielectric ceramic described above may notcontain Ca, Sr, Zr, or Hf. Thus, one characteristic is that Gd and Mgare present. As described above, Gd is contained at 3.5 mol % or less,whereas Mg is contained at 3.5 mol % or less.

The rare earth element Gd is brought into the A sites of a perovskitestructure represented by ABO₃ as a solid solution, whereas Mg is broughtinto B sites of the perovskite structure, thereby achieving highreliability. However, there is a problem in that the substitutioncontents of Gd and Mg are low and both are 3.5 mol % or less, therebyresulting in the inability to achieve sufficient reliability.

On the other hand, International Publication No. WO2004/067473 disclosesa grain diameter of preferably 2.5 μm or less, more preferably 1.5 μm orless, and even more preferably 1 μm or less, for the grain diameters ofcrystal grains in the dielectric ceramic as a sintered body. In allcases, the crystal grains in the sintered body for the dielectricceramic described in International Publication No. WO2004/067473, have alarge grain diameter of 0.9 μm or more. Accordingly, as thinning isprogressed, the number of crystal grains present in each dielectricceramic layer will be reduced, easily leading to a problem withreliability.

In addition, while a method of increasing the substitution amounts ofthe rare earth element such as Gd and the element such as Mg isconceivable in order to improve reliability, the crystal grains willlikely be further increased in this case.

SUMMARY OF THE INVENTION

Therefore, an object of the invention is to provide a dielectric ceramicand a method for manufacturing the dielectric ceramic, which can solvethe problems described above.

Another object of the invention is to provide a laminated ceramiccapacitor composed with use of the dielectric ceramic mentioned above.

In order to solve the technical problems described above, the inventionis directed to a dielectric ceramic including a main componentcontaining a barium titanate based composite oxide represented by thegeneral formula: (Ba_(1-h-m-x)Ca_(h)Sr_(m)Re_(x))_(k)(Ti_(i-n-y)Zr_(n)M_(y)) O₃, where Re is at least one of La, Ce, Pr, Nd,Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y, M is at least one of Mg,Ni, Mn, Al, Cr, and Zn, and respective relationships of 0.05≦x≦0.50,0.02≦y≦0.3, 0.85≦k≦1.05, 0≦h≦0.25, 0≦m≦0.50, and 0≦n≦0.40 are satisfied;and an accessory component as a sintering aid, wherein the average graindiameter of crystal grains in a sintered body is 0.6 μm or less.

It is to be noted that the grain diameter is obtained by observing across section of the dielectric ceramic with use of a scanning electronmicroscope, and the average grain diameter is obtained by averaging thegrain diameters of, for example, 30 grains.

The invention is also directed to a method for manufacturing thedielectric ceramic as described above.

A method for manufacturing a dielectric ceramic according to theinvention includes first step of obtaining a reactant containing abarium titanate based composite oxide represented by the generalformula: (Ba_(1-h-m-x)Ca_(h)Sr_(m)Re_(x))_(k)(Ti_(1-n-y)Zr_(n)M_(y))O₃,where Re is at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er,Tm, Yb, Lu, and Y, M is at least one of Mg, Ni, Mn, Al, Cr, and Zn, andrespective relationships of 0.05≦x≦0.50, 0.02≦y≦0.3, 0.85≦k≦1.05,0≦h≦0.25, 0≦m≦0.50, and 0≦n≦0.40 are satisfied; second step of preparingan accessory component as a sintering aid; third step of mixing theaccessory component prepared in second step into the reactant obtainedin first step; and fourth step of calcining the mixture obtained inthird step.

In the first step, multiple raw material powders including a BaCO₃powder are calcined in order to obtain the reactant in such a way thatunreacted BaCO₃ remains so that the intensity ratio between the (111)diffraction peak of BaCO₃ and the (110) diffraction peak of BaTiO₃ byX-ray diffraction analysis of the calcined powder is 15/1000 or more and200/1000 or less, and is carried forward so that the third step mixturecontains the unreacted reactant.

The invention is also directed to a laminated ceramic capacitorincluding: a capacitor main body composed of a plurality of laminateddielectric ceramic layers and a plurality of internal electrodes formedalong specific interfaces between the dielectric ceramic layers; and aplurality of external electrodes formed in different positions from eachother on an external surface of the capacitor main body and electricallyconnected to specific ones of the internal electrodes.

In the laminated ceramic capacitor according to the invention, thedielectric ceramic layers contain the dielectric ceramic according tothe invention.

Although the dielectric ceramic according to the invention containsrelatively large amounts of Re and M in the composition of the maincomponent, grain growth is suppressed, and the crystal grains have asmall average grain diameter of 0.6 μm or less. Thus, even when thedielectric ceramic layers are thin and have a thickness of, for example,less than 3 μm in the laminated ceramic capacitor, excellentreliability, and more particularly, excellent lifetime characteristic,can be achieved.

More specifically, first, since the Re and M are contained in relativelarge amounts, which are effective for enhancing the reliability,excellent reliability can be achieved. In addition, although the Re andM are contained in relative large amounts, which act to promote graingrowth while being effective for enhancing the reliability, grain growthis suppressed to realize an average grain diameter of 0.6 μm or less,and thus, also in this regard, the reliability can be improved.

In accordance with the method for manufacturing a dielectric ceramicaccording to the invention, the unreacted BaCO₃ moderately remains sothat the intensity ratio between the (111) diffraction peak of BaCO₃ andthe (110) diffraction peak of BaTiO₃ by X-ray diffraction analysis ofthe calcined powder is 15/1000 or more and 200/1000 or less, in thecalcination procedure of the first step for obtaining the reactant,thereby suppressing grain growth. Therefore, the average grain diameterof crystal grains can be 0.6 μm or less in the obtained dielectricceramic as a sintered body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically illustrating a laminatedceramic capacitor 1 composed with use of a dielectric ceramic accordingto the invention.

DETAILED DESCRIPTION OF THE INVENTION

First, a laminated ceramic capacitor 1 with a dielectric ceramicaccording to the invention applied will be described with reference toFIG. 1.

The laminated ceramic capacitor 1 includes a capacitor main body 5composed of a plurality of laminated dielectric ceramic layers 2 and aplurality of internal electrodes 3 and 4 formed along the specificinterfaces between the dielectric ceramic layers 2. The internalelectrodes 3 and 4 mainly contain, for example, Ni.

First and second external electrodes 6 and 7 are formed in differentpositions on the external surface of the capacitor main body 5. Theexternal electrodes 6 and 7 mainly contain, for example, Ag or Cu. Thelaminated ceramic capacitor 1 shown in FIG. 1 has the first and secondexternal electrodes 6 and 7 formed on the respective end surfaces of thecapacitor main body 5 opposed to each other. As for the internalelectrodes 3 and 4, the plurality of first internal electrodes 3 iselectrically connected to the first external electrode 6, whereas theplurality of second internal electrodes 4 is electrically connected tothe second external electrode 7. These first and second internalelectrodes 3 and 4 are arranged alternately with respect to the stackingdirection.

It is to be noted that the laminated ceramic capacitor 1 may be atwo-terminal laminated ceramic capacitor provided with the two externalelectrodes 6 and 7, or may be a multi-terminal laminated ceramiccapacitor provided with a large number of external electrodes.

The dielectric ceramic layers 2 are composed of the following dielectricceramic as a feature of the invention.

That is, the dielectric ceramic layers 2 includes a main componentcontaining a barium titanate based composite oxide represented by thegeneral formula:(Ba_(1-h-m-x)Ca_(h)Sr_(m)Re_(x))_(k)(Ti_(1-n-y)Zr_(n)M_(y))O₃, where Reis at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb,Lu, and Y, M is at least one of Mg, Ni, Mn, Al, Cr, and Zn, andrespective relationships of 0.05≦x≦0.50, 0.02≦y≦0.3, 0.85≦k≦1.05,0≦h≦0.25, 0≦m≦0.50, and 0≦n≦0.40 are satisfied; and an accessorycomponent as a sintering aid, wherein the average grain diameter ofcrystal grains in the sintered body is 0.6 μm or less.

Although the dielectric ceramic described above contains relativelylarge amounts of Re and M in the composition of the main component,grain growth is suppressed, and the crystal grains have a small averagegrain diameter of 0.6 μm or less. Thus, even when the dielectric ceramiclayers 2 are thin and have a thickness of, for example, less than 3 μm,excellent reliability, and more particularly, excellent lifetimecharacteristic can be achieved.

Next, a preferred embodiment of a method for manufacturing a dielectricceramic according to the invention will be described while describing amethod for manufacturing the laminated ceramic capacitor 1 shown in FIG.1.

First, a raw material powder for the dielectric ceramic constituting thedielectric ceramic layers 2 is prepared. This raw material is preferablymanufactured as follows.

First, carried out is first step of obtaining a reactant containing abarium titanate based composite oxide represented by the generalformula: (Ba_(1-h-m-x)Ca_(h)Sr_(m)Re_(x))_(k)(Ti_(1-n-y)Zr_(n)M_(y))O₃,where Re is at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er,Tm, Yb, Lu, and Y, M is at least one of Mg, Ni, Mn, Al, Cr, and Zn, inwhich the respective relationships of 0.05≦x≦0.50, 0.02≦y≦0.3,0.85≦k≦1.05, 0≦h≦0.25, 0≦m≦0.50, and 0≦n≦0.40 are satisfied.

In this first step, calcining multiple raw material powders including aBaCO₃ powder is carried out in order to obtain the composite oxidereactant. More specifically, in addition to the BaCO₃ powder, powders ofcompounds each containing the elements included in the general formulamentioned above are mixed to provide a predetermined composition ratio,calcined in air, and then ground.

The calcination conditions, such as the calcination temperature, arecontrolled in such a way that the intensity ratio between the (111)diffraction peak of BaCO₃ and the (110) diffraction peak of BaTiO₃ byX-ray diffraction analysis of the calcined powder is 15/1000 or more and200/1000 or less so that a predetermined amount of unreacted BaCO₃remains. It is to be noted that it is conceivable that in addition tothe calcination conditions, the specific surface area of a starting rawmaterial, the grinding conditions, and the like will also affect theresidual amount of the unreacted carbonate. This unreacted BaCO₃ acts toadvantageously suppress grain growth in the calcination step describedbelow.

The second step is carried out for preparing an accessory component as asintering aid, such as MnO or SiO₂.

Next, a third step is carried out to combine the accessory componentprepared in second step into the reactant obtained in first step. Themixture obtained in third step is a raw material powder for thedielectric ceramic, which also includes the unreacted BaCO₃.

Next, a slurry is manufactured by adding an organic binder and a solventto the mixture obtained in third step, that is, the raw material powderfor the dielectric ceramic, and mixing them, and this slurry is used toform ceramic green sheets serving as the dielectric ceramic layers 2.

Then, a conductive paste containing, for example, Ni, as a conductivecomponent is printed on specific ceramic green sheets to form aconductive paste film serving as an internal electrode 3 or 4.

Then, a plurality of ceramic green sheets with the conductive pastefilms formed as described above are stacked, and ceramic green sheetswith no conductive paste film formed are stacked so as to sandwich theceramic green sheets with the conductive paste films, and subjected topressure bonding, followed by cutting, if necessary, thereby obtaining araw laminated body serving as a capacitor main body 5. In this rawlaminated body, the conductive paste films have end edges exposed ateither end surface.

Then, a fourth step is carried out for calcination of the mixtureobtained in third step. More specifically, the step is carried out forcalcination of the raw laminated body in a reducing atmosphere. Thisstep provides a sintered capacitor main body 5 as shown in FIG. 1, andin the capacitor main body 5, the ceramic green sheets constitute thedielectric ceramic layers 2 composed of the dielectric ceramic, and theconductive paste films constitute the internal electrode 3 or 4.

The dielectric ceramic as the sintered body constituting the dielectricceramic layers 2 has an average crystal grain diameter of 0.6 μm orless.

Then, external electrodes 6 and 7 are formed respectively by baking of aconductive paste containing, for example, Ag, on respective end surfacesof the capacitor main body 5, so as to be electrically connected torespective exposed end edges of the internal electrodes 3 and 4.

Then, if necessary, a plating film such as nickel or copper is formed onthe external electrodes 6 and 7, and a plating film such as solder ortin is formed thereon.

As described above, the laminated ceramic capacitor 1 is completed.

Next, the invention will be described more specifically with referenceto experimental examples.

Experimental Example 1

As staring raw materials for the main component for a dielectricceramic, respective powders of BaCO₃, CaCO₃, SrCO₃, TiO₂, ZrO₂, Gd₂O₃,and MgO were prepared. It is to be noted that a powder with a specificsurface area of 11 m²/g and a powder with a specific surface area of 13m²/g were selected respectively as the BaCO₃ powder and the TiO₂ powder.

Next, each of the starting raw materials was weighed so as to achieve acomposition ratio of (Ba_(0.89)Ca_(0.01)Sr_(0.01)Gd_(0.10))(Ti_(0.93)Zr_(0.01)Mg_(0.06)) O₃.

Next, for samples 1 to 4 shown in Table 1, 100 g of the weighed rawmaterial powders were each mixed and ground with 130 g of water in a wetmanner for 50 hours in a ball mill with PSZ balls of 0.8 mm in diameter,and then dried, calcined in air for 2 hours at each temperature in therange of 950 to 1150° C. shown in the column “Calcination Temperature”of Table 1, to obtain a barium titanate based raw material powder.

Samples 5 to 8 shown in Table 1 are comparative examples.

For sample 5, the same process as in the case of samples 1 to 4 wascarried out except that a temperature of 1150° C. was applied uponcalcination, as shown in the column “Calcination Temperature” of Table1.

For sample 6, the same process as in the case of samples 1 to 4 wascarried out except that a temperature of 400° C. was applied uponcalcination, as shown in the column “Calcination Temperature” of Table1.

For sample 7, 100 mol parts of BaTiO₃ powder with 1 mol part of CaCO₃powder, 1 mol part of SrCO₃ powder, 1 mol part of ZrO₂ powder, 10 molparts of Gd₂O₃ powder, and 6 mol parts of MgO powder added to was usedas a raw material powder without calcination.

Sample 8 was obtained by adding MgO powder after initial mixing andcalcination, rather than during the mixing or the calcination. Morespecifically, the calcination temperature of 1100° C. was applied to acomposition of (Ba_(0.89)Ca_(0.01)Sr_(0.01)Gd_(0.10))(Ti_(0.99)Zr_(0.01))O₃, as shown in the column “Calcination Temperature”of Table 1 to carry out the process up to the calcination, and then theMgO powder was added to achieve a content of 6 mol parts.

Next, the intensity ratio between the (111) diffraction peak of BaCO₃and the (110) diffraction peak of BaTiO₃ was evaluated by X-raydiffraction analysis (XRD) for the calcined powders. The results areshown in the column of the “Peak Ratio” in Table 1.

Next, to 100 mol parts of the barium titanate based raw material powderaccording to each sample, 1 mol part of BaCO₃ for correction of theBa/Ti ratio was further added, and 1 mol part of MnO powder and 2 molparts of SiO₂ powder were each added as raw materials for accessorycomponents serving as sintering aids, followed by wet mixing andgrinding in a ball mill, and then drying.

Next, the dried mixed powder was mixed with a polyvinyl butyral basedbinder and mixed in a wet manner in a ball mill to prepare a slurry.This slurry was subjected to sheet forming by a doctor blade method torectangular ceramic green sheets. It is to be noted here that thethicknesses of the ceramic green sheets to be formed were controlled soas to achieve respective thicknesses of 1.5 μm, 3 μm and 4.5 μm forcalcined dielectric ceramic layers obtained from the ceramic greensheets, as shown in Table 1.

Next, a conductive paste mainly containing Ni was printed on the ceramicgreen sheets to form conductive paste films serving as internalelectrodes.

Next, 102 sheets of the ceramic green sheets with the conductive pastefilms formed were stacked so that the drawn ends of the conductive pastefilms are alternately arranged, thereby obtaining a raw laminated bodyserving as a capacitor main body.

Next, the raw laminated body was heated to a temperature of 350° C. in aN₂ atmosphere to burn out the binder, and then calcined at a temperaturewithin the range of 1000 to 1200° C. in a reducing atmosphere composedof a H₂—N₂—H₂O gas with an oxygen partial pressure of 10⁻⁹ to 10⁻¹² MPato obtain a sintered capacitor main body.

Next, an Ag paste containing a B₂O₃—Li₂O—SiO₂—BaO based glass frit wasapplied to both end surfaces of the sintered capacitor main body, andbaked at a temperature of 600° C. in a N₂ atmosphere to form externalelectrodes electrically connected to the internal electrodes, therebyobtaining a laminated ceramic capacitor as a sample.

The laminated ceramic capacitor thus obtained had outside dimensions of3.2 mm in length and 1.6 mm in width.

Next, the laminated ceramic capacitors according to each sample wereevaluated for the “grain diameter” and the “failure rate”.

The “Grain Diameter” shown in Table 1 was obtained by observing a crosssection in the stacking direction of the capacitor main body accordingto each sample with use of a scanning electron microscope, selecting 30or more crystal grains, measuring the grain diameters of the respectivecrystal grains, and averaging the grain diameters.

The “Failure Rate” shown in Table 1 indicates reliability excellence,and shows the number of failed samples after a lapse of 50 hours withrespect to 100 samples, through the evaluation of the insulationdegradation lifetime by subjecting the laminated ceramic capacitoraccording to each sample to a high temperature load test. In the hightemperature load test, a voltage was applied to the laminated ceramiccapacitor according to each sample at a temperature of 190° C. so as toprovide an electric field intensity of 30 kV/mm, and when the insulationresistance after the test was decreased by three or more orders ofmagnitude as compared with the insulation resistance before the test,the sample was determined as a failed sample.

TABLE 1 Grain 1.5 μm 3 μm 4.5 μm Sample Calcination Peak Ratio DiameterFailure Failure Failure Number Temperature (° C.) BaCO₃/BaTiO₃ (μm) RateRate Rate 1  950 200/1000  0.47  2/100 2/100 0/100 2 1000 162/1000  0.28 0/100 0/100 0/100 3 1050 95/1000 0.35  3/100 2/100 0/100 4 1100 18/10000.58  9/100 3/100 0/100  5* 1150 10/1000 0.98 100/100 11/100  0/100  6* 400 — 1.7 100/100 77/100  31/100   7* — — 0.45 100/100 100/100  56/100  8* 1100  0/1000 0.20 100/100 100/100  100/100 

Table 1 shows that when the peak ratio is 15/1000 or more and 200/1000or less, as in the case of samples 1 to 4, a dielectric ceramic can beobtained which meets the requirement of an average grain diameter of 0.6μm or less.

In addition, for samples 1 to 4 which meet the size requirement, evenwhen the dielectric ceramic layers were thinned to have a thickness of1.5 μm, excellent reliability was achieved, as indicated by a failurerate within 10%. The effect of the improvement in reliability can besaid to be more significant with an increase in the thinness of thelayers, because for comparative example sample 5, the failure rate issharply increased in the sample with dielectric ceramic layers of 1.5 μmin thickness, as compared with the respective samples with dielectricceramic layers of 3 μm and 4.5 μm in thickness.

For the comparative example sample 6, it was not possible to determinethe peak ratio because BaTiO₃ was not synthesized in the calcinationstep. In addition, the grain diameter was large in the sintered body,with an increased failure rate.

In addition, the grain diameter of sample 7 was small because Gd as theRe element and Mg as the M element were not sufficiently present in thegrains. The failure rate was extremely high.

For sample 8, the grain diameter was small because Mg as the M elementwas not sufficiently present in the grains. However, the failure ratewas all 100/100.

Experimental Example 2

As staring raw materials supposed to be main components for a dielectricceramic, respective powders of BaCO₃, CaCO₃, SrCO₃, TiO₂ and ZrO₂,respective powders of La₂O₃, CeO₂, Pr₆O₁₁, Nd₂O₃, Sm₂O₃, EU₂O₃, Gd₂O₃,Tb₄O₇, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, Lu₂O₃, and Y₂O₃ as oxides ofRe, and respective powders of MgO, NiO, MnO, Al₂O₃, Cr₂O₃, and ZnO asoxides of M were prepared. It is to be noted that the powders with thesame specific surface areas as selected in Experimental Example 1 wereselected as the BaCO₃ powder and the TiO₂ powder.

Next, the starting raw materials were weighed so as to achievecomposition ratios shown in Table 2 in terms of(Ba_(1-h-m-x)Ca_(h)Sr_(m)Re_(x))_(k) (Ti_(1-n-y)Zr_(n)M_(y)) O₃. Next,the weighed raw material powders were mixed and ground in a wet mannerin the same way as in Experimental Example 1, and then dried, calcinedin air for 2 hours at each temperature in the range of 950 to 1150° C.shown in the column “Calcination Temperature” of Table 2 to obtain abarium titanate based raw material powder.

Next, the intensity ratio between the (111) diffraction peak of BaCO₃and the (110) diffraction peak of BaTiO₃ of the calcined powders wasevaluated by X-ray diffraction analysis (XRD) in the same way as inExperimental Example 1. The results are shown in the column of the “PeakRatio” in Table 2.

Next, a MnO powder and a SiO₂ powder as accessory components serving assintering aids were added in the mol parts per 100 mol parts of thebarium titanate based raw material powder according to each sample shownin the column “Subsequent Addition” of Table 2, and laminated ceramiccapacitors according to each sample were obtained in the same way as inExperimental Example 1. It is to be noted that the calcined dielectricceramic layers were made to have a thickness of 1.5 μm for all of thesamples in Experimental Example 2.

Next, the “Grain Diameter” and “Failure Rate” were evaluated for thelaminated ceramic capacitors according to each sample, as shown in Table2, in the same manner as in the case of Experimental Example 1.

TABLE 2 Sample Number K h m n Re x M y  9 0.85 0 0 0.05 Gd 0.06 Mg 0.0510 1.00 0 0.01 0.03 Gd 0.10 Mg 0.05 11 1.01 0.01 0.01 0 Gd 0.15 Mg 0.0812 1.02 0 0.02 0.01 Gd 0.20 Mg 0.12 13 1.03 0.01 0 0.02 Gd 0.30 Mg 0.1414 1.04 0.02 0.03 0 Gd 0.10 Mg 0.08 15 1.03 0.25 0 0 Gd 0.08 Mg 0.03 161.03 0 0.50 0 Gd 0.10 Mg 0.05 17 1.03 0 0 0.40 Gd 0.06 Mg 0.04 18 1.03 00 0.02 Gd 0.05 Mg 0.03 19 1.03 0.01 0.02 0 Gd 0.50 Mg 0.30  20* 1.030.01 0.01 0.10 Gd 0.04 Mg 0.02  21* 1.03 0.01 0.01 0.10 Gd 0.06 Mg 0.0122 1.05 0.01 0.01 0.30 La 0.30 Mg 0.20 23 1.03 0.1 0.3 0.20 Ce 0.30 Mg0.20 24 1.01 0.05 0.02 0.20 Pr 0.20 Mg 0.15 25 0.90 0.01 0.01 0.10 Nd0.20 Mg 0.10 26 1.03 0.1 0 0.40 Sm 0.20 Mg 0.15 27 1.03 0.05 0.03 0.20Eu 0.15 Mg 0.10 28 1.03 0.05 0.10 0 Tb 0.15 Mg 0.08 29 1.03 0.06 0 0.01Dy 0.10 Mg 0.04 30 1.03 0.10 0.10 0 Ho 0.10 Mg 0.03 31 1.03 0.15 0 0.01Y 0.10 Mg 0.03 32 1.04 0.20 0.50 0 Er 0.07 Mg 0.03 33 1.03 0.20 0.30 0Tm 0.07 Mg 0.03 34 1.03 0.25 0.01 0 Yb 0.05 Mg 0.02 35 1.03 0.25 0.01 0Lu 0.05 Mg 0.02 36 1.03 0.01 0.01 0 Sm 0.08 Al 0.06 37 1.03 0 0.02 0.01Sm 0.08 Cr 0.06 38 1.03 0 0 0.01 Gd 0.15 Ni 0.08 39 1.03 0.02 0 0 Gd0.10 Mn 0.04 40 1.03 0.01 0.01 0 Gd 0.12 Mg:Mn 0.04:0.04 41 1.03 0 00.02 Dy 0.10 Zn 0.08 42 1.03 0 0 0.02 Dy 0.06 Mn 0.02 43 1.03 0.25 0.010 Dy 0.08 Al:Mn 0.02:0.03 44 1.03 0.01 0.01 0.01 Sm:Dy 0.10:0.10 Mg:Zn0.10:0.03 45 1.03 0 0.01 0.02 Gd:Y 0.08:0.08 Ni:Mn 0.08 46 1.03 0.010.04 0 Dy:Y 0.10:0.05 Ni:Al 0.05:0.03 47 1.03 0.03 0 0.01 Gd:Dy:Yb0.10:0.05:0.05 Mn 0.10 Subsequent Addition Calcination Grain Sample (molpart) Temperature Peak Ratio Diameter Failure Number MnO SiO₂ (° C.)BaCO₃/BaTiO₃ (μm) Rate  9 1.00 2.00 950 175/1000 0.51 0/100 10 1.00 2.00950 181/1000 0.47 0/100 11 1.00 2.00 1000 182/1000 0.45 0/100 12 1.002.00 1000 184/1000 0.44 0/100 13 1.00 2.00 1000 189/1000 0.48 0/100 141.00 2.00 1000 146/1000 0.37 0/100 15 1.00 2.00 950 192/1000 0.50 0/10016 1.00 2.00 1000 140/1000 0.38 0/100 17 1.00 2.00 1000 162/1000 0.451/100 18 1.00 2.00 950 185/1000 0.50 1/100 19 1.00 2.00 1050 121/10000.45 1/100  20* 1.00 2.00 950 186/1000 1.1 100/100   21* 1.00 2.00 950184/1000 1.3 100/100  22 1.00 2.00 1050 129/1000 0.40 5/100 23 1.00 2.001050 120/1000 0.44 3/100 24 1.00 2.00 1050 125/1000 0.46 4/100 25 1.002.00 1050 124/1000 0.48 4/100 26 1.00 2.00 1000 181/1000 0.50 1/100 271.00 2.00 1000 180/1000 0.50 0/100 28 1.00 2.00 1000 147/1000 0.44 0/10029 1.00 2.00 1000 144/1000 0.36 0/100 30 1.00 2.00 1000 152/1000 0.330/100 31 1.00 2.00 1000 160/1000 0.35 3/100 32 1.00 2.00 1000 148/10000.42 3/100 33 1.00 2.00 1000 158/1000 0.43 5/100 34 1.00 2.00 1000141/1000 0.38 3/100 35 1.00 2.00 1000 136/1000 0.38 4/100 36 1.00 2.001000 120/1000 0.45 1/100 37 1.00 2.00 1000 122/1000 0.47 1/100 38 1.002.00 1000 170/1000 0.33 0/100 39 0.00 2.00 1000 180/1000 0.36 0/100 400.00 2.00 1000 168/1000 0.35 0/100 41 1.00 2.00 1000 180/100  0.47 5/10042 0.00 2.00 950 188/1000 0.55 5/100 43 0.00 2.00 1000 132/1000 0.422/100 44 1.00 2.00 1000 172/1000 0.38 3/100 45 0.00 2.00 1000 157/10000.40 0/100 46 1.00 2.00 1000 152/1000 0.39 0/100 47 0.00 2.00 1000159/1000 0.44 0/100

Table 2 shows that as long as the contents of the respective elementsconstituting(Ba_(1-h-m-x)Ca_(h)Sr_(m)Re_(x))_(k)(Ti_(1-n-y)Zr_(n)M_(y))O₃ satisfythe respective relationships of 0.05x≦0.50, 0.02≦y≦0.3, 0.85≦k≦1.05,0≦h≦0.25, 0≦m≦0.50, and 0≦n≦0.40, a dielectric ceramic which meets therequirement of an average grain diameter of 0.6 μm or less can beobtained when the peak ratio is 15/1000 or more and 200/1000 or less,regardless of the types or combination of the Re element and M element.Furthermore, an excellent insulation degradation lifetime characteristiccan be achieved with an extremely low failure rate, even when thedielectric ceramic layers are thin and have a thickness of 1.5 μl, withthe average grain diameter of 0.6 μm or less.

On the other hand, in samples 20 and 21 with either the Re content x orthe M content y outside the range 0.05≦x≦0.50 or 0.02≦y≦0.3, it wasdifficult to keep the grain diameters of 0.6 μm or less. Therefore,samples 20 and 21 exhibited a failure rate of 100/100, and an inferiorinsulation degradation lifetime.

In the case of compositions such as samples 20 and 21 described above,it has been confirmed that if the calcination temperature is lowered,the unreacted reactant will also diffuse and participate in a solidsolution formation during main calcination, resulting in an inability tosuppress grain growth.

When the Re element was weighed as in the general formula, on theassumption of barium titanate brought into A sites of a solid solutionin the experimental examples described above, no problem will be causedagainst advantageous effects of the present invention even when Re isbrought into B sites of a solid solution in an actually synthesizedpowder.

1. A sintered dielectric ceramic having crystal grains and comprising: amain component comprising a barium titanate based composite oxiderepresented by the general formula:(Ba_(1-h-m-x)Ca_(h)Sr_(m)Re_(x))_(k)(Ti_(1-n-y)Zr_(n)M_(y))O₃, where Reis at least one member of the group consisting of La, Ce, Pr, Nd, Sm,Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y, M is at least one member ofthe group consisting of Mg, Ni, Mn, Al, Cr, and Zn, 0.05≦x≦0.50,0.02≦y≦0.3, 0.85≦k≦1.05, 0≦h≦0.25, 0≦m≦0.50, and 0≦n≦0.40; and asintering aid accessory component, wherein the average grain diameter ofthe crystal grains in the sintered body is 0.6 μm or less.
 2. Thesintered dielectric ceramic according to claim 1, wherein 0.06≦x≦0.3,0.03≦y≦0.2, 1.00≦k≦1.04, 0≦h≦0.20, 0≦m≦0.3, 0≦n≦0.3, and wherein theaverage grain diameter of crystal grains in the sintered body is 0.58 μmor less.
 3. The sintered dielectric ceramic according to claim 1,wherein the average grain diameter of crystal grains in the sinteredbody is 0.50 μm or less.
 4. The sintered dielectric ceramic according toclaim 1, wherein M comprises Mg.
 5. The sintered dielectric ceramicaccording to claim 3, wherein Re comprises Gd.
 6. The sintereddielectric ceramic according to claim 1, wherein Re comprises Gd.
 7. Abarium titanate based composite oxide represented by the generalformula: (Ba_(1-h-m-x)Ca_(h)Sr_(m)Re_(x))_(k) (Ti_(1-n-y)Zr_(n)M_(y))O₃, where Re is at least one member of the group consisting of La, Ce,Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y, M is at least onemember of the group consisting of Mg, Ni, Mn, Al, Cr, and Zn,0.05≦x≦0.50, 0.02≦y≦0.3, 0.85≦k≦1.05, 0≦h≦0.25, 0≦m≦0.50, and 0≦n≦0.40;wherein the intensity ratio between the (111) diffraction peak of BaCO₃and the (110) diffraction peak of BaTiO₃ by X-ray diffraction analysisof the calcined powder is 15/1000 to 200/1000.
 8. The barium titanatebased composite oxide according to claim 7, wherein 0.06≦x≦0.3,0.03≦y≦0.2, 1.00≦k≦1.04, 0≦h≦0.20, 0≦m≦0.3, 0≦n≦0.3, and the intensityratio between the (111) diffraction peak of BaCO₃ and the (110)diffraction peak of BaTiO₃ by X-ray diffraction analysis of the calcinedpowder is 120/1000 to 189/1000.
 9. The barium titanate based compositeoxide according to claim 7, wherein M comprises Mg.
 10. The bariumtitanate based composite oxide according to claim 9, wherein Recomprises Gd.
 11. The barium titanate based composite oxide according toclaim 7, wherein Re comprises Gd.
 12. A method for manufacturing adielectric ceramic comprising: providing a mixture of a barium titanatebased composite oxide represented by the general formula:(Ba_(1-h-m-x)Ca_(h)Sr_(m)Re_(x))_(k)(Ti_(1-n-y)Zr_(n)M_(y))O₃, where Reis at least one member of the group consisting of La, Ce, Pr, Nd, Sm,Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y, M is at least one member ofthe group consisting of Mg, Ni, Mn, Al, Cr, and Zn, 0.05≦x≦0.50,0.02≦y≦0.3, 0.85≦k≦1.05, 0≦h≦0.25, 0≦m≦0.50, and 0≦n≦0.40, and theintensity ratio between a (111) diffraction peak of BaCO₃ and a (110)diffraction peak of BaTiO₃ by X-ray diffraction analysis of the calcinedpowder is 15/1000 to 200/1000; and an accessory component sintering aid;and calcining the mixture in a reducing atmosphere.
 13. The methodaccording to claim 12, wherein 0.06≦x≦0.3, 0.03≦y≦0.2, 1.00≦k≦1.04,0≦h≦0.20, 0≦m≦0.3, and 0≦n≦0.3.
 14. The method according to claim 12,wherein M comprises Mg.
 15. The method according to claim 14, wherein Recomprises Gd.
 16. The method according to claim 12, wherein Re comprisesGd.
 17. A laminated ceramic capacitor comprising: a capacitor main bodycomprising a plurality of laminated dielectric ceramic layers and aplurality of internal electrodes each disposed at different interfacesbetween adjacent dielectric ceramic layers; and at least two externalelectrodes disposed at different positions on an external surface of thecapacitor main body and electrically connected to different ones of theinternal electrodes, wherein the dielectric ceramic layers comprise thedielectric ceramic according to claim
 1. 18. A laminated ceramiccapacitor comprising: a capacitor main body comprising a plurality oflaminated dielectric ceramic layers and a plurality of internalelectrodes each disposed at different interfaces between adjacentdielectric ceramic layers; and at least two external electrodes disposedat different positions on an external surface of the capacitor main bodyand electrically connected to different ones of the internal electrodes,wherein the dielectric ceramic layers comprise the dielectric ceramicaccording to claim
 2. 19. A laminated ceramic capacitor comprising: acapacitor main body comprising a plurality of laminated dielectricceramic layers and a plurality of internal electrodes each disposed atdifferent interfaces between adjacent dielectric ceramic layers; and atleast two external electrodes disposed at different positions on anexternal surface of the capacitor main body and electrically connectedto different ones of the internal electrodes, wherein the dielectricceramic layers comprise the dielectric ceramic according to claim
 4. 20.A laminated ceramic capacitor comprising: a capacitor main bodycomprising a plurality of laminated dielectric ceramic layers and aplurality of internal electrodes each disposed at different interfacesbetween adjacent dielectric ceramic layers; and at least two externalelectrodes disposed at different positions on an external surface of thecapacitor main body and electrically connected to different ones of theinternal electrodes, wherein the dielectric ceramic layers comprise thedielectric ceramic according to claim 6.